Christopher John Brennan was born in Sydney in 1870, the son of Irish migrants. Brennan was educated at a number of schools and seemed to be bound for the priesthood until he abandoned his vocation before leaving St Ignatius College, Riverview, for the University of Sydney. At University Brennan read deeply in the classics and philosophy, graduating with first-class honours in 1891. A James King of Irrawang Travelling Scholarship enabled him to study at the University of Berlin in 1892-94. But the distraction of Berlin's cultural and intellectual milieu and a love affair with his landlady's daughter, Anna Elisabeth Werth, saw him return to Sydney without the expected doctorate. Brennan married Anna Werth in Sydney in 1897, but the marriage was strained by 1907 after the birth of four children and the arrival of Brennan's mother-in-law. Brennan turned to the cafe society of Sydney where he became a formidable presence with his incomparable intellect and wit.
When Brennan abandoned his religious vocation he began a spiritual quest for a similar absolute. Returning to Sydney in 1897, steeped in the poetry of Mallarme and other European symbolists, Brennan decided to pursue this absolute through the composition of verse. This pursuit culminated in the publication of Poems (1913), Brennan's most admired work. Most critics interpret Poems as a pursuit for Eden and argue that it adheres to Mallarme's concept of the livre compose, a collection of poems conceived and executed as a whole.
Brennan was offered a long awaited academic appointment at the University of Sydney in 1909. His difficulty in attaining this position may have been caused by his heavy drinking and the eroticism of his first printed book of verse, XXI Poems (1897). But despite his reputation he was appointed associate professor in German and comparative literature in 1920. This success was short lived. University officials could not tolerate the scandal of Brennan's divorce and his relationship with Violet Singer, the subject of Brennan's most well-known love poems. Brennan was dismissed by the University Senate in 1925, the same year that Violet Singer was hit and killed by a tram. His subsequent despair and destitution were eased by occasional teaching and the generosity of his friends and former students. But despite giving up alcohol after a period of increasing ill-health, Brennan died in 1932 soon after returning to the Catholic faith he had neglected since entering university.